U.S. patent application number 12/159861 was filed with the patent office on 2008-12-04 for smart radiation detector module.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONICS N. V.. Invention is credited to Marc A. Chappo, Randall P. Luhta, Rodney A. Mattson.
Application Number | 20080298541 12/159861 |
Document ID | / |
Family ID | 38257074 |
Filed Date | 2008-12-04 |
United States Patent
Application |
20080298541 |
Kind Code |
A1 |
Mattson; Rodney A. ; et
al. |
December 4, 2008 |
Smart Radiation Detector Module
Abstract
An ionizing radiation detector module (22) includes a detector
array (200), a memory (202), signal processing electronics (208), a
communications interface (210), and a connector (212). The memory
contains detector performance parameters (204) and detector
correction algorithms (206). The signal processing electronics
(208) uses the detector performance parameters (204) to correct
signals from the detector array (200) in accordance with the
detector correction algorithms (206).
Inventors: |
Mattson; Rodney A.; (Mentor,
OH) ; Chappo; Marc A.; (Elyria, OH) ; Luhta;
Randall P.; (Highland Heights, OH) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
595 MINER ROAD
CLEVELAND
OH
44143
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONICS N.
V.
Eindhoven
NL
|
Family ID: |
38257074 |
Appl. No.: |
12/159861 |
Filed: |
January 4, 2007 |
PCT Filed: |
January 4, 2007 |
PCT NO: |
PCT/US07/60083 |
371 Date: |
July 2, 2008 |
Current U.S.
Class: |
378/19 |
Current CPC
Class: |
A61B 6/585 20130101;
A61B 6/032 20130101 |
Class at
Publication: |
378/19 |
International
Class: |
A61B 6/03 20060101
A61B006/03 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 16, 2006 |
US |
60766385 |
Claims
1. In a computed tomography apparatus including an x-ray source, a
plurality of x-radiation sensitive detector modules and a
reconstructor which generates volume space data indicative of
x-radiation detected by the detector modules, the detector modules
comprising; an x-radiation sensitive detector array which generates
electrical signals in response to x-radiation detected thereby; a
memory which contains a first parameter indicative of a measured
performance characteristic of the detector module; circuitry in
operative communication with the memory which corrects the
electrical signals as a function of the first parameter so as to
generate corrected detector signals.
2. The apparatus of claim 1 wherein the detector array includes a
plurality of detector pixels and wherein the first parameter
includes a parameter indicative of a measured performance
characteristic of individual pixels in the array.
3. The apparatus of claim 2 wherein the parameter identifies
inoperative pixels.
4. The apparatus of claim 3 wherein the circuitry uses a temporally
corresponding signal from a pixel in the neighborhood of an
inoperative pixel to correct for the inoperative pixel.
5. The apparatus of claim 2 wherein the measured performance
characteristic is crosstalk between pixels in the array.
6. The apparatus of claim 1 wherein the performance characteristic
is measured prior to installation of the detector module in the
computed tomography apparatus.
7. The apparatus of claim 6 wherein the detector module includes a
component, wherein the first parameter is indicative of a measured
performance characteristic of the component, and wherein the
performance characteristic of the component is measured prior to
installation of the component in the detector module.
8. The apparatus of claim 1 wherein the detector module includes a
communication interface in operative communication with the memory
and adapted to receive data indicative of the measured performance
characteristic from a source external to the detector module.
9. The apparatus of claim 1 wherein in the memory includes a second
parameter indicative of a measured performance characteristic of
the detector module and wherein the detector module includes a
communication interface in operative communication with the memory
and adapted to communicate the second parameter to a device
external to the detector module, whereby an external device may
correct the corrected detector signals as a function of the second
parameter.
10. The apparatus of claim 1 wherein the detector module includes a
computer readable storage medium containing instructions which,
when executed by a computer processor, cause the computer processor
to carry out a method which includes using the first parameter to
correct the electrical signals.
11. (canceled)
12. (canceled)
13. (canceled)
14. An x-ray detector module for use in an imaging apparatus, the
detector module comprising: a plurality of x-ray sensitive detector
pixels which generate signals in response to detected x-rays; a
memory which contains data indicative of the performance of the
detector pixels; signal correction circuitry in operative
communication with the memory and the detector pixels, wherein the
signal correction circuitry corrects the detector pixel signals as
a function of the data so as to generate corrected signals; an
electrical connector for selectively electrically connecting the
detector module to the imaging apparatus.
15. The detector module of claim 14 wherein the data includes data
indicative of a first performance characteristic which is
determined prior to installation of the detector module in the
imaging apparatus.
16. The detector module of claim 15 wherein the data includes data
indicative of a second performance characteristic which is
determined subsequent to installation of the detector module in the
imaging apparatus.
17. The detector module of claim 16 wherein the second performance
characteristic is detector offset.
18. The detector module of claim 15 wherein the data includes data
indicative of a plurality of performance characteristics which are
determined prior to installation of the detector module in the
imaging apparatus, and wherein the performance characteristics
include at least one of afterglow, crosstalk, linearity, offset,
and pixel operative status.
19. The detector module of claim 14 wherein the signal correction
circuitry includes digital circuitry.
20. (canceled)
21. The apparatus of claim 19 wherein the signal correction
circuitry and the memory are disposed in single ASIC.
22. The detector module of claim 14 wherein the detector module
includes a communication interface in operative communication with
the memory and adapted to receive the data from a source external
to the detector module.
23. The detector module of claim 14 wherein the signal correction
circuitry corrects the detector pixel signals as a function of a
first portion of the data and wherein the detector module includes
a communication interface adapted to communicate a second portion
of the data to a device external to the detector module, whereby a
further correction may applied by a device external to the detector
module.
24. The detector module of claim 14 wherein the detector pixels
include back contact photodiodes.
25. (canceled)
26. An imaging apparatus comprising: an ionizing radiation source;
a radiation detector which detects radiation emitted by the
radiation source and including a plurality of detector modules,
each of the detector modules including: means for generating
electrical signals indicative of detected radiation; means for
storing data indicative of the performance of the detector modules;
means for using the data to correct the electrical signals; means
for selectively connecting the detector module to the detector; a
reconstructor which generates volumetric data indicative of the
radiation detected by the radiation detector.
Description
[0001] The present invention finds particular application to
radiation detectors used in computed tomography (CT) scanners. It
also finds application to other radiation sensitive detectors, and
especially in situations where it is desirable to correct for
variations in detector performance.
[0002] CT scanners have proven to be invaluable in providing
information indicative of the internal structure of an object. In
medical imaging, for example, CT scanners are widely used to
provide images and other information about the physiology of human
patients. Recent years have seen the rapid adoption of multi-slice
CT, as increasing the number of slices or channels can have a
number of advantages, such as an improved ability to scan the heart
and other moving portions of the anatomy, shorter scan times,
improved scanner throughput, improved axial resolution and
coverage, and the like.
[0003] One consequence of this trend, however, is that CT detector
modules are becoming increasingly complex and expensive. Indeed,
the detector is often one of the most expensive components, if not
the most expensive component, of a CT scanner.
[0004] By way of one example, state of the art CT scanners are
designed to provide as many as 128 slices in one revolution. In
such a system, a typical detector module may contain as may as 2048
(16.times.128) individual detector pixels. The detector would
typically contain a number of modules, so that an exemplary
detector may contain as many as 80,000 individual detector pixels.
In turn, each detector pixel typically includes a scintillator, a
photodiode, mechanical supports, optical and electrical interfaces,
and associated electronic signal conditioning circuitry. Each of
these items can influence the performance characteristics of the
detector pixel and the detector module as a whole.
[0005] As the number of detector pixels increases, it becomes
increasingly likely that variations in detector performance will
become significant. For example, individual detector pixels may
have differing performance characteristics or may even be entirely
inoperative. Moreover, even for a nominally identical detector
design, detector performance characteristics may vary from vendor
to vendor, or even lot to lot.
[0006] It is desirable to reduce the impact of these variations.
For example, manufacturing yields can be improved, and costs
reduced, if performance variations can be identified and corrected,
rather than discarding or reworking a detector module. Viewed from
one perspective, detector yield can be improved by allowing for
relatively wider performance limits. Viewed from another
perspective, identifying and correcting for performance variations
will, for a given set of detector acceptance criteria, generally
provide improved detector performance. Servicing of detectors
modules can also be simplified by reducing the situations in which
it is necessary to replace a detector module. Where it is necessary
to replace a detector module, it is desirable to reduce the need
for additional detector or scanner calibrations.
[0007] Some corrections may be made by the reconstruction computer
as part of the image reconstruction process. As will be
appreciated, however, another trend has been a demand for ever
shorter reconstruction times, together with a requirement to
reconstruct ever increasing amounts of data and numbers of image
slices. Unfortunately, the task of identifying and applying the
necessary corrections during reconstruction tends to increase
overall system complexity and can also have a deleterious impact on
reconstructor performance.
[0008] Aspects of the present invention address these matters, and
others.
[0009] According to a first aspect of the invention, a computed
tomography apparatus includes an x-ray source, a plurality of
x-radiation sensitive detector modules and a reconstructor which
generates volume space data indicative of x-radiation detected by
the detector modules. The detector modules include an x-radiation
sensitive detector array which generates electrical signals in
response to x-radiation detected thereby, a memory which contains a
first parameter indicative of a measured performance characteristic
of the detector module, and circuitry in operative communication
with the memory which corrects the electrical signals as a function
of the first parameter so as to generate corrected detector
signals.
[0010] According to another aspect of the invention, an x-ray
detector module is adapted for use in an imaging apparatus which
utilizes a plurality of detector modules disposed so as to form a
tiled two dimensional array of detector pixels. The detector module
includes a plurality of x-ray sensitive detector pixels which
generate signals in response to detected x-rays. The pixels are
arranged for installation in the tiled two-dimensional array. The
detector module also includes a memory which contains data
indicative of the performance of the detector pixels, signal
correction circuitry in operative communication with the memory and
the detector pixels, and an electrical connector for selectively
electrically connecting the detector module to the imaging
apparatus. The signal correction circuitry corrects the detector
pixel signals as a function of the data so as to generate corrected
signals.
[0011] According to another aspect of the invention, an imaging
apparatus includes an ionizing radiation source, a radiation
detector which detects radiation emitted by the radiation source,
and a reconstructor which generates volumetric data indicative of
the radiation detected by the radiation detector. The radiation
detector includes a plurality of detector modules, each of which
includes means for generating electrical signals indicative of
detected radiation, means for storing data indicative of the
performance of the detector modules, means for using the data to
correct the electrical signals, and means for selectively
connecting the detector module to the detector.
[0012] Those skilled in the art will appreciate still other aspects
of the present invention upon reading and understanding the
attached figures and description.
[0013] The present invention is illustrated by way of example and
not limitation in the figures of the accompanying drawings, in
which like references indicate similar elements and in which:
[0014] FIG. 1 depicts a CT scanner.
[0015] FIG. 2 is a functional block diagram of a detector module
for a CT scanner.
[0016] FIG. 3 depicts a process for characterizing a detector
module.
[0017] FIG. 4 depicts an exemplary detector correction process.
[0018] With reference to FIG. 1, a CT scanner 10 includes a
rotating gantry portion 18 which rotates about an examination
region 14. The gantry 18 supports a radiation source 12 such as an
x-ray tube. The gantry 18 also supports an x-ray sensitive detector
20 which subtends an arc on the opposite side of the examination
region 14. X-rays produced by the x-ray source 12 traverse the
examination region 14 and are detected by the detector 20. An
object support 16 supports an object such as human patient in the
examination region 14. The support 16 is preferably movable in
coordination with the rotation of the gantry 18 so as to provide
helical scanning.
[0019] The detector 20 includes an arcuate array of detector
modules 22 arranged so as to form a two dimensional array of
detector pixels. The detector modules are preferably arranged in a
tiled array in which the pixels in an array abut the pixels in
adjacent arrays. In one implementation, the detector 20 includes
one hundred twenty eight (128) or more slices. Suitable detector
implementations are further described in commonly assigned U.S.
Pat. No. 6,510,195, entitled Solid State X-Radiation Detector
Module and Mosaics Thereof, and an Imaging Method and Apparatus
Employing the Same, which is expressly incorporated by reference
herein in its entirety, although other detector implementations are
also possible. Note also that the arrays may be irregular. For
example, pixels in one or more rows or columns may be offset from
one another.
[0020] A so-called fourth generation scanner configuration, in
which the detector 20 spans an arc of 360 degrees and remains
stationary while the x-ray source 12 rotates, as well as flat panel
detectors, may also be implemented. Detector having greater or
lesser number of slices may likewise be implemented.
[0021] As will be further discussed below, readout electronics
associated with each detector module 22 receive signals originating
from the various detector pixels and provide signal conditioning,
analog to digital conversion, multiplexing, and like functionality.
Certain detector specific performance information is also stored in
memory associated with detector module 22 and is preferably used to
provide a corrected detector output signal.
[0022] A data acquisition system 24 preferably carried by the
rotating gantry 18 receives output signals from a plurality of
detector modules 22 and provides additional multiplexing, data
communication, and like functionality. A reconstructor 26
reconstructs the data obtained by the detector 20 to form
volumetric image data indicative of the object under
examination.
[0023] A general purpose computer serves an operator console 44.
The console 44 includes a human-readable output device such as a
monitor or display and an input device such as a keyboard and
mouse. Software resident on the console allows the operator to
control the operation of the scanner by establishing desired scan
protocols, initiating and terminating scans, viewing and otherwise
manipulating the volumetric image data, and otherwise interacting
with the scanner.
[0024] A controller 28 coordinates the various scan parameters as
necessary to carry out a desired scan protocol, including x-ray
source 12 parameters, movement of the patient couch 16, and
operation of the data acquisition system 26.
[0025] FIG. 2 is a functional block diagram of a detector module
22. The detector module 22 includes one more detector arrays 200,
readout electronics 60, and one or more connectors 212. The
detector array(s) 200, readout electronics 60, and connector are
mounted to or carried by a suitable printed circuit board or other
substrate for assembly in the detector 20. The detector module 22
may also include multiple substrates.
[0026] The detector array 200 includes an n.times.m array of
detector pixels, with each detector pixel including a scintillator
in optical communication with a photodiode. Back contact or back
illuminated photodiodes facilitate the fabrication of relatively
larger arrays, although front illuminated or other photodiode
structures may also be used. Other detector array 200
implementations, such as multiple energy, solid state, or direct
conversion detectors, are also contemplated. In one embodiment,
each detector array 200 includes a 16.times.16 array of detector
pixels, and the detector module 22 includes eight (8) detector
arrays 200 arranged so as to form a 16.times.128 array.
[0027] The readout electronics 60, which receives and processes
signals generated by the various detector pixels, can be
implemented as a microprocessor based application specific
integrated circuit (ASIC) which includes an operatively connected
memory 202, signal processing electronics 208, and communications
interface 210.
[0028] The signal processing electronics 208 includes multiplexing,
amplification and filtering, analog to digital conversion, signal
correction, and like circuitry for processing the signals generated
by the various detector pixels.
[0029] The memory 202 includes detector performance parameters 204
and detector correction algorithms 206. Exemplary detector
performance parameters 204 include one or more of detector
afterglow, cross talk, linearity, pixel operative/inoperative
status, gain, offset, and silicon hole trapping data, although
information relating to additional or different performance
characteristics may also be stored. Depending on the particular
performance characteristic and the characteristics of a particular
detector, the relevant parameters are stored individually for each
detector pixel. One or more of the parameters may also be stored
for use in connection with the detector array 200 or the detector
module 22 as a whole, especially where the performance
characteristic is expected to be relatively uniform for the various
detector pixels in the detector array 200 or the detector module 22
as a whole.
[0030] The correction algorithms 206 are stored as computer
readable instructions which, when carried out by the
microprocessor, use the relevant detector performance parameters
204 to carry out the desired corrections. In this regard, it should
be noted that it is not necessary that the parameters 204 and
algorithms 206 be stored in the same physical memory. Exemplary
detector correction algorithms include corrections for detector
afterglow, cross talk, linearity, inoperative detector elements,
gain, offset, and silicon hole trapping corrections, although
additional or different corrections may be applied. A temperature
correction may also be applied at the detector level. Some or all
of the corrections are preferably applied in real time during
operation of the scanner 10 so that corrected detector signals are
supplied to the reconstructor 26.
[0031] Also associated with each detector module 22 is a serial
number or similar identifier. Additional information, such as date
codes, manufacturer or vendor information, or the like may also be
associated with the detector module 22. The information may be
stored in the memory 202. Some or all of the information may also
be provided on a bar code or other computer readable designator,
human readable designator, traveler, or the like associated with
the detector module 22 or its individual components. Such an
arrangement is particularly advantageous where some or all of the
components of a detector module 22 are characterized prior to
assembly in the detector module 22. In such a situation, the
performance characteristics associated with a particular component
may be stored in a database and the performance parameters 204
loaded into the memory 202 of the appropriate detector module 22 in
a subsequent manufacturing step.
[0032] The communication interface 210 provides communications
between the data acquisition circuitry 24, the memory 202, and the
signal processing electronics 208.
[0033] One or more electrical connectors 212 allow the detector
module 22 to be electrically connected to the detector 20 during
the manufacturing process. The connector(s) 212 preferably also
facilitate field replacement of the detector nodule 22, if
needed.
[0034] It should also be noted that the readout electronics 60 do
not necessarily include a microprocessor. In such an
implementation, the various corrections may be implemented using
one more digital signal processors (DSPs), field programmable gate
arrays (FPGAs), or other suitable digital or analog electronic
circuitry. The readout electronics 60 may also be implemented using
multiple ASICs, integrated circuits, discrete components, or a
combination thereof.
[0035] In addition, one or more detector modules 22 may be combined
to form a still larger detector module. In such an implementation,
some or all of the readout electronics 60 may be apportioned
between the detector modules 22 and the larger module.
[0036] An exemplary process for characterizing a detector module 22
during manufacturing is depicted in FIG. 3. At 302, a unique
identifier is assigned to the detector module. Where detector
components are characterized individually, unique identifiers are
also assigned to the individual components.
[0037] The detector performance is characterized at step 304. As
noted above, the characterization may be performed at different
assembly levels. For example, it may be desirable to characterize
certain of the parameters at the component level, others at the
module level, or still others at the detector 20 or scanner 10
levels.
[0038] One exemplary characterization is a test for crosstalk
between detector pixels, which is more readily performed at the
detector module level. Another is a test for inoperative pixels, in
which inoperative pixels are identified. Such a test is again more
readily performed at the detector module level. Detector modules 22
having several inoperative pixels in proximity to each other, or
inoperative edge pixels for which sufficient neighboring pixel data
is unavailable, are rejected. Otherwise, the locations of the
inoperative pixels are identified.
[0039] Detector offset, on the other hand, is often evaluated at
the beginning of an actual scan. Other performance tests, such as
those for detector gain, afterglow, linearity, and the like are
well known to those skilled in the art and may also be readily
implemented at the desired level.
[0040] The test results are stored at step 306, for example in a
test database, in a traveler which accompanies the particular
component, or the like. In this regard, it should be noted that the
temporal sequence in which the individual components or modules are
tested is not critical. Of course, testing performed at a given
assembly level should be performed after the various components
have been assembled to form the desired assembly level.
[0041] At step 308, the detector performance parameters 204 are
loaded into the memory 202 of a given detector module. Where one or
more components were characterized at the component level, the
characteristics of the particular component are obtained from the
database. In one implementation, the performance parameters 204 are
communicated to the detector module 22 via the communications
interface 210. Note that the communication of the relevant
parameters may be performed at a convenient level in the assembly
process, for example before or after the detector module 22 has
been installed in the detector 20 or the scanner 10. Moreover, some
or all of the parameters 204 may be stored in the memory 202 before
it is installed in the particular detector module 22. It may also
be desirable to load different correction algorithms 206 into the
memory 202 depending on the characteristics of a particular
detector module 22.
[0042] Final detector 20 and scanner 10 characterization and
testing is performed as needed at step 310.
[0043] As noted above, the demands on the reconstructor 26 can be
reduced if some or all of the corrections are performed on the
detector signals in or near real time before they are presented to
the reconstructor 26. An exemplary correction process is depicted
in FIG. 4. While FIG. 4 describes the process for a single detector
pixel, it will of course be understood that the other detector
pixels are similarly corrected.
[0044] At 402, a given detector pixel generates a signal indicative
of the radiation detected during a scan. The signal converted to
digital form at step 404.
[0045] A detector offset correction is performed at step 406. As
noted above, detector offset is typically measured at the beginning
of every scan in the absence of x-rays from the source, with the
offset information stored in the memory 202.
[0046] A gain correction is performed at step 408 using data from
the memory 202, Similarly, a cross talk correction is performed at
step 410. In one implementation, the signals generated by detector
pixels or modules having a relatively high cross talk are corrected
to reduce cross talk effects. In another implementation, cross talk
is added to detector pixels or modules exhibiting a relatively low
cross talk. An inoperative pixel correction is applied at step 412.
For pixels identified as defective, temporally corresponding
signals from one or more neighboring detector pixels are
interpolated in or near real time to produce a signal which
approximates that of the inoperative pixel. This signal is used to
replace the signal from the otherwise inoperative pixel. Of course,
still additional, different, subsets of the above corrections may
also be applied.
[0047] In any case, the corrections are applied in or near real
time during scanning so that corrected signals are supplied to the
reconstructor 26.
[0048] Still other corrections may be performed upstream. For
example, a global or system gain correction, which is typically
based on a scanner air calibration, is applied by the reconstructor
26 at 414.
[0049] It is also not necessary to perform all of the necessary
corrections at the detector module level. Thus, some or all of the
detector performance parameters 202, for example those relating to
detector linearity and afterglow, may be uploaded to the scanner 10
via the communication interface 210 as part of the scanner
calibration process, with the corrections performed by the
reconstructor 26 or other upstream. Alternatively, the module
identifier may be uploaded and the corresponding parameters
obtained from a database.
[0050] The performance characteristics of a particular detector
pixel or detector module 22 may also change during the life of the
scanner. As just one example, a previously functional detector
pixel may become inoperative. Once the inoperative pixel has been
identified, typically during servicing of the scanner, the location
of the pixel is communicated to the relevant memory 202 via the
communication interface 210. The locations of other inoperative
pixels may also be identified by querying the detector module 22.
Alternately, the signal processing electronics 208 may be
configured to automatically detect inoperative pixels during
calibration or otherwise during operation of the scanner. If the
number or location of inoperative pixels meets a desired acceptance
criteria, the output of the particular pixel is synthesized as
described above during operation of the scanner. If the acceptance
criteria are not satisfied, the detector module 22 is preferably
repaired or replaced. A similar procedure may be applied to account
for changes in other detector parameters.
[0051] Of course, modifications and alterations will occur to
others upon reading and understanding the preceding description. It
is intended that the invention be construed as including all such
modifications and alterations insofar as they come within the scope
of the appended claims or the equivalents thereof.
* * * * *